Radioactive and stable isotopes

Question 1

Isotopes

Answer 1

different forms of atoms of the same element.
i.e same atomic number, different mass numbers

e.g H has 3 isotopes. H, H2(deuterium), H3(tritium)

C11(radioactive),C12(99%),C13,C14(radioactive)

Question 2

Types of radioactive emission

Answer 2

alpha, beta, gamma

alpha - helium atom, +2 charge (no electrons)
beta - electrons -ve or positrons +ve
gamma - photons, uncharged.

Question 3

Alpha radiation

Answer 3

emitted only by elements of mass >140
formation:
U238 -> Th234 + He4 (2+ve)

Question 4

Beta radiation

Answer 4

neutron -> proton + e- + antineutrino
P32 -> S32 + e- + antineutrino
Zn65 -> Cu65 + e- + antineutrino

Question 5

Electrons and positrons

Answer 5

They have a range of energies H3 has a lower energy than C14

Question 6

Gamma radiation

Answer 6

EM radiation/photon
Residue from beta emission
I131 -> Xe131 -> Xe131 + gamma

Question 7

X ray production

Answer 7

Electron capture. A proton in the nucleus captures an electron from the innermost electron shell, the K shell.
This forms a neutron and an antineutrino.
An electron form an outer shell moves into replace this electron, giving out energy, in the form of x ray.

Question 8

Radiactive decay (first order)

Answer 8

Does not involve interaction between 2 atoms. The rate is not affected by anything, unless bombarded by sub atomic particles.

Question 9

Exponential radiactive decay

Answer 9

Half life - time of which nuclei undergo radioactive decay, this exponentially slows down.

Question 10

First order process equation

Answer 10

The rate of radioactive decay of N atoms is proportional to the number of radioactive atoms present.
hence, we get the equation t1/2 = 0.693/lantha

Question 11

Quantifying radiactivity

Answer 11

Curie - amount of radioactivity released by a gram of radium

1Curie = 3.7 x 10^10 Bq

Question 12

Specific activity

Answer 12

The number of disintegration/unit mass/unit time.

e.g Ci/g , Ci/mole.

Question 13

Countin efficiency

Answer 13

how much radioactivity if observed (cpm) counts per min.

Question 14

Detection of radiation

Answer 14

1) Liquid scintillation counting
2) Geiger-Muller counting
3) Autoradiography

Question 15

Liquid scintillation counting

Answer 15

e- + fluor -> light emission -> Light is measured
The flashes of light are referred to as scintillation
Used for H3, C14, S35

compound dissolved in solvent
beta particles collide with solvent molecules
excited solvent molecules return to the ground state, releasing light
Photons have short wavelength, not detected well by photocells
So fluor substance is added to amplify the effect.

cons: Quenching
Colour quenching, is substance absorbed certain wavelenth, light is not emitted
Chemical quenching - compound reacts with solvent
Point quenching- doesnt dissolve (in a lump)
dilution quenching- too much liquid into fluid.

Question 16

Cerenkov counting

Answer 16

Fuel rods giving off cerenkov radiation

-Hard beta emitters with energy > 0.26 MeV

Question 17

Geiger-muller tubes

Answer 17

Contains an inert gas and a quenching gas, there is a mica window at the end and anode in the center.

Electrong goes through mica window, in which the inertt gas is ionized, positively charged particle goes to cathode and electron goes through to anode.
This produces a voltage which is measured.

Question 18

Autoradigraphy

Answer 18

Geiger will display that there is radioactivity, not quantify.

1) Radioactive sample
2) place x-ray film with photographic emulsion (contain silver halide)
3) Silver halide is processed (activated) to silver.
4) Film is processed

Advantages:
radiactive chemical/compound will behave the same as unlabelled version
Sensitive 1x10^-15 moles
turnover studies, biochemical patchways

Disadvantages
different stability of covalent bond between radioactive and normal atom adjoined to it, so the bond strengths may differ. Usually fixed by putting radioactive molecule on site that does not take place on reaction.
Caution to prevent placing radioactive material that will undergo chemical exchange with the environment.
radioactive compound does not change to smaller precursor materials, unreadable
Decay, e.g P32 has 2 weeks half life.

Question 19

Uses of radioactivity

Answer 19

South,North,Western blotting
electro mobility shift assay
metabolic pathways
pulse chase
PROTEIN BINDING
RADIOAMUNOASSAY
isotope dilution -> conc. of compound

Question 20

Southern blotting

Answer 20

Measured DNA molecules
Cleave sample
Gel in alkaline solution
Blot to membrane
DNA in membrane is hybridised with P32 DNA, membrane is developed.

Question 21

Radioactive probe synthesis

Answer 21

Radioactive ATP

Cutting with restriction enzymes
Kienow DNA polymerase and radioactive ATP

Question 22

Sickle cell detection

Answer 22

Southern blot
B-chain of haem, a substitution occurs
Hence, in haem protein, instead of Glutamate, we have Valine
Use MsT2, cut B-chain of normal haem.
Southern blotting, look at sizes of fragments.

Question 23

Northern blotting

Answer 23

Used to study RNA
To tell if gene is expressed

Run RNA to gel
blot to membrane
Probed with P32 labelled single stranded DNA probe

mRNA is only produced when a protein is being expressed.

Question 24

Western Blotting

Answer 24

1) SDS page
2) Blot to Membrane
3) Add primary antibody that binds to protein of interest
4) Add radioactive protein A or G (bacterial proteins)
5) Bind to antibodies.
6) Film expresses bands where proteins are

Question 25

EMSA

Answer 25

Used to study DNA and DNA binding proteins
DNA by itself will move faster down the gel, than a DNA + DNA binding. Uses polyacrylamide gel
DNA + binding = slower
DNA = faster

Question 26

Metabolic pathway analysis

Answer 26

A -> B -> C
Can use radioactivity to study this
A is given radioactive material.

Question 27

Mechanism of Rifampicin (treat tuberculosis)

Answer 27

1) RNA polymerase from e.coli, mixed with DNA
2) Nucleotide triphosphate with radioactive cTP
3) Allowed polermase to work
4) Purified RNA
5) Measured radioactivity.

Question 28

Pulse chase analysis

Answer 28

1) grow cells, incubate with S–methoinine (radioactive)
2) Cells lysed and lysomal enzyme cathepsin D was purified, run on gel and subjected to autoradiography
3) Shows protein modification

Question 29

Chain termination (DNA seq)

Answer 29

uses radioactive ddNTP, normal dNTP and gel electrophoresis and run a gel electrophoresis